1. Field of the Invention
The present invention relates to testing of well bore fluids and, more particularly, a method of measuring changes in the well bore fluid due to dilution from connate water invasion or surface dilution.
2. Description of the Background
In well drilling, completion and workover operations, particularly well drilling operations, there is a need to know whether there has been any dilution of the well bore fluid, e.g. the drilling mud, from downhole formation water, i.e. connate water, or from surface dilution. Such dilution can change the density of the well bore fluid rendering it unsuitable for use and, in many cases, unsafe. For example, dilution of the drilling mud may lower its density to the point where it cannot maintain sufficient hydrostatic pressure in the well bore to prevent a blowout. Dilution by connate water may also be important as an indication of the nature of the formation through which the drilling is taking place. Furthermore, in workover and completion operations, it is desirable and often times necessary to know whether there has been invasion of connate water into the completion or workover fluid.
In U.S. Pat. No. 3,407,042, there is described a method of testing well samples, such as a fluid or core material, to determine whether there has been invasion of the well sample by the drilling fluid. In the method described in the patent, nitrate ion is added to the drilling mud and the concentration of nitrate ion found in the well sample compared with the concentration of that originally in the drilling mud. In the method described in the patent, the well sample is tested to determine invasion from the drilling mud. However, there is no testing of the drilling fluid per se to determine dilution by invasion either from surface fluids or connate water. Moreover, the method described in the patent utilizes a colorimetric test method which can pose difficulties when the drilling fluid contains colored additives.